Distributed fiber sensors and systems that rely on Rayleigh scattering are being adopted for many applications, including but not limited to, structure health monitoring (SHM), geotechnical engineering, power lines, oil and gas pipe lines, and oil and gas wells. In particular, these sensors and systems can employ Rayleigh scattering mechanisms to measure temperature, pressure, strain, acoustic waves and other parameters with a spatial resolution of less than 1 m.
Conventional approaches that rely on Rayleigh scattering often employ telecommunication grade optical fibers in distributed fiber sensors and systems to obtain these measurements (e.g., temperature, pressure, strain, etc.). Distributed fiber sensors and systems that rely on such optical fibers suffer from various drawbacks. For example, the optical power of the launched signal can be limited by low threshold, nonlinear effects in the fiber. As a result, the scattered signal is often low, especially at the far end of the fiber away from the transmission end. As another example, attenuation in these optical fibers can also limit the scattered signal strength at the far end of the fiber, especially for fiber spans of tens of kilometers. Further, the optical power in telecommunication grade fibers that are configured for single mode operation is often low due to the small numerical aperture of such fibers. All of these effects tend to reduce the signal-to-noise ratio associated with comparative distributed fiber sensors and systems that employ telecommunication grade optical fibers.
As distributed fiber sensors and systems that rely on optical fibers and Rayleigh scattering mechanisms continue to be employed in various applications (e.g., geotechnical engineering, power lines, etc.), the use of these sensors and systems is generally limited by their effectiveness at longer distances.
There is therefore a need for distributed fiber sensors and fiber sensor systems that employ optical fibers that can transmit optical signals with less signal loss and higher signal-to-noise ratios. More particularly, there is a need for enhanced distributed fiber sensors and sensor systems that employ fibers that rely on Rayleigh scattering mechanisms and are designed and controlled for predetermined distances.